Reduction of leachable beta-glucan levels from cellulose-containing filter materials

ABSTRACT

Treatment methods for reduction of (1→3)-β-D-glucan leachables from cellulose-containing filter materials are described.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation Application of U.S. application Ser. No. 17/235,071, filed Apr. 20, 2021, which is a Continuation Application of U.S. application Ser. No. 16/316,890, filed Jan. 10, 2019, now U.S. Pat. No. 11,014,031, which is a US National Stage Application of International Application No. PCT/US2017/057878, filed Oct. 23, 2017, which claims the benefit of priority of U.S. Provisional Patent Application No. 62/413,013, filed Oct. 26, 2016, each of which is incorporated by reference herein in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to the reduction of the level of (1→3)-β-D-glucan leachables from cellulose-containing filter materials.

BACKGROUND OF THE DISCLOSURE

Cellulose-containing media and filters are widely used in biopharmaceutical and plasma purification processes for removal of impurities from target molecules. (1→3)-β-D-glucan (“beta-glucans”) is an inherent impurity in the cellulosic matrix and can leach out into the product stream during the filtration of proteins and similar components. Regulatory agencies require biopharmaceutical manufacturers to closely monitor levels of beta-glucan impurities and maintain them below a defined threshold. Elevated levels of beta-glucan leachables originating from filters, particularly ones being used further downstream in the process, are a cause of concern due to patient safety and regulatory reasons. In addition, serum-based product manufacturers are required to maintain beta-glucan leachable levels below threshold amounts.

SUMMARY OF THE DISCLOSURE

Among the various aspects of the present disclosure is the provision of a method for reducing the amount of leachable beta-glucans in a cellulose-containing filter material.

Briefly, therefore, the present disclosure is directed to a method for reducing the amount of leachable beta-glucans in a cellulose-containing filter material, the method comprising treating the filter material with a solution comprising a carbonate salt, an organic carbonate (such as a carbonate ester), or carbonic acid.

Another aspect of the disclosure is the provision of a cellulose-containing filter material treated in accordance with the methods described herein, wherein the filter material has a reduced amount of leachable beta-glucans as compared to an untreated filter material.

Another aspect of the disclosure is the provision of a method for preparing a biopharmaceutical or a plasma derivative having a reduced amount of leached beta-glucan, the method comprising treating the biopharmaceutical or a plasma derivative by contact with a cellulose-containing filter material treated in accordance with the methods described herein.

Another aspect of the disclosure is the provision of a biopharmaceutical or a plasma derivative prepared by contacting the same with a cellulose-containing filter material treated in accordance with the methods described herein, wherein the biopharmaceutical or a plasma derivative comprises a reduced amount of leached beta-glucans as compared to an untreated biopharmaceutical or a plasma derivative.

Other objects and features will be in part apparent and in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the disclosure will become more fully apparent from the following detailed description, appended claims, and accompanying drawings, wherein the drawings illustrate features in accordance with exemplary aspects of the disclosure, and wherein:

FIG. 1 is an exemplary schematic of bench scale setup for investigation of specialized flushes.

FIG. 2 is an exemplary schematic of bench scale setup for investigation of specialized flushes in recirculation mode.

FIG. 3 is a graph illustrating an effect of specialized flushes on leached beta-glucan levels in a product pool.

FIG. 4 is a graph illustrating VPro Comparative performance of carbonate flushed and standard flushed VPF (Monoclonal antibody A, VPF Lot C4AA98988).

FIG. 5 is a graph illustrating VPro Comparative performance of carbonate flushed and standard flushed VPF (Monoclonal antibody B, VPF Lot C3AA43491).

FIG. 6 is a graph illustrating a comparison of Sodium and Potassium carbonate for removal of beta-glucans from depth filters.

FIG. 7 is a graph illustrating a Pareto chart for size of effect analysis.

FIG. 8 is a graph illustrating measured versus predicted beta-glucan leachable level.

FIG. 9 is a contour plot illustrating low hold values.

FIG. 10 is a contour plot illustrating intermediate hold values.

FIG. 11 is a contour plot illustrating high hold values.

FIG. 12 is a graph illustrating the effect of different volume to area ratio of flushing solution in recirculation mode.

FIG. 13 is a graph illustrating the reduction of leached beta-glucan from unprocessed cellulose pulp using sodium and potassium hydroxide.

ABBREVIATIONS AND DEFINITIONS

The following definitions and methods are provided to better define the present disclosure and to guide those of ordinary skill in the art in the practice of the present disclosure. Unless otherwise noted, terms are to be understood according to conventional usage by those of ordinary skill in the relevant art.

All publications, patents and patent applications cited herein, whether supra or infra, are hereby incorporated by reference in their entirety to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference.

The term “comprising,” which is synonymous with “including,” “containing,” or “characterized by,” is inclusive or open-ended and does not exclude additional, unrecited elements or method steps.

The term “consisting essentially of” limits the scope of a claim to the specified materials or steps “and those that do not materially affect the basic and novel characteristic(s)” of the claimed invention.

The term “consisting of” as used herein, excludes any element, step, or ingredient not specified in the claim.

It must be noted that, as used in this specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to a “component” includes one, two or more such components.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although a number of methods and materials similar or equivalent to those described herein can be used in the practice of the present invention, the preferred materials and methods are described herein.

DETAILED DESCRIPTION OF THE DISCLOSURE

One aspect of the present disclosure is directed to a method for reducing the amount of leachable beta-glucans in a cellulose-containing filter material. It has been advantageously discovered that the methods described herein, and treated filter materials produced thereby, can significantly reduce the amount of beta-glucans that commonly leach into a product pool (i.e., the components collected following a filtration pass) such as a biopharmaceutical or plasma derivative.

In general, the methods and filters described herein are capable of reducing the level of leachable beta-glucans in a cellulose-containing filter material by greater than 10%, greater than 20%, greater than 30%, greater than 40%, greater than 50%, greater than 60%, greater than 70%, greater than 80%, greater than 90%, greater than 95%, or greater than 99%. Such leached beta-glucans can be detected, for example, in the filtrate following the treatment process (i.e., as an indicator of treatment efficacy). Where treated cellulose-containing filter materials described herein are subsequently employed in biopharmaceutical or plasma derivative processing, this reduction in leachable beta-glucan levels may translate, for example, to a biopharmaceutical or plasma derivative product having a beta-glucan impurity level of less than 1000 pg/ml, less than 900 pg/ml, less than 800 pg/ml, less than 700 pg/ml, less than 600 pg/ml, less than 500 pg/ml, less than 400 pg/ml, less than 300 pg/ml, less than 200 pg/ml, or less than 100 pg/ml. The lower limit of beta-glucan impurities is not particularly limited, and may preferably be less than 50 pg/ml or even less.

Treatment Solution

The methods described herein involve treating a cellulose-containing filter material with a carbonate-containing solution. In general, treatment of the filter material is carried out by soaking, circulating, recirculating, washing, flushing, passing through, or otherwise contacting the filter material with the solution in order to remove leachable beta-glucans therefrom, as discussed in further detail below.

The carbonate-containing solution includes a carbonate salt, an organic carbonate, or carbonic acid. Combinations of carbonate salts, organic carbonates, and/or carbonic acid may also be employed.

In some embodiments, for example, the solution includes a carbonate salt. Exemplary carbonate salts include ammonium carbonate, ammonium hydrogen carbonate, barium carbonate, calcium carbonate, iron carbonate, lithium carbonate, magnesium carbonate, manganese carbonate, potassium carbonate, potassium hydrogen carbonate, sodium carbonate, sodium hydrogen carbonate, and mixtures thereof. In one particular embodiment, the carbonate salt is selected from the group consisting of ammonium carbonate, calcium carbonate, iron carbonate, magnesium carbonate, manganese carbonate, potassium carbonate, sodium carbonate, and mixtures thereof. In another particular embodiment, the carbonate salt is selected from the group consisting of ammonium carbonate, calcium carbonate, potassium carbonate, sodium carbonate, and mixtures thereof. In one preferred embodiment, the carbonate salt is sodium carbonate, potassium carbonate, or a mixture thereof.

In other embodiments, for example, the solution includes an organic carbonate. The organic carbonates generally have the formula: RO[(CO)O]_(n)R, wherein each R is independently a substituted or unsubstituted, straight-chain or branched aliphatic, aromatic/aliphatic (araliphatic) or aromatic hydrocarbon radical having 1 to 20 C atoms. The two radicals R may also be joined to one another to form a ring. The two radicals R may be the same or different; in one particular embodiment they are the same. In this embodiment, R is preferably an aliphatic hydrocarbon radical and more preferably a straight-chain or branched alkyl radical having 1 to 5 C atoms, or a substituted or unsubstituted phenyl radical. R in this case is a straight-chain or branched, preferably straight-chain (cyclo)aliphatic, aromatic/aliphatic or aromatic, preferably (cyclo)aliphatic or aromatic, more preferably aliphatic hydrocarbon radical having 1 to 20 C atoms, preferably 1 to 12, more preferably 1 to 6, and very preferably 1 to 4 carbon atoms. Examples of such radicals are methyl, ethyl, isopropyl, n-propyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-hexyl, n-heptyl, n-octyl, n-decyl, n-dodecyl, n-tetradecyl, n-hexadecyl, n-octadecyl, n-eicosyl, 2-ethylhexyl, cyclopentyl, cyclohexyl, cyclooctyl, cyclododecyl, phenyl, o- or p-tolyl or naphthyl. These radicals R may be the same or different; they are preferably the same. The radicals R may also be joined to one another to form a ring. Examples of divalent radicals R of this kind are 1,2-ethylene, 1,2-propylene, and 1,3-propylene. Generally speaking, n is an integer from 1 to 5, preferably from 1 to 3, more preferably from 1 to 2. The carbonates may preferably be simple carbonates of the general formula RO(CO)OR, i.e., n in this case is 1.

Examples of suitable carbonates comprise aliphatic, aromatic/aliphatic or aromatic carbonates such as ethylene carbonate, 1,2- or 1,3-propylene carbonate, diphenyl carbonate, ditolyl carbonate, dixylyl carbonate, dinaphthyl carbonate, ethyl phenyl carbonate, dibenzyl carbonate, dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, di-n-butyl carbonate, diisobutyl carbonate, dipentyl carbonate, dihexyl carbonate, dicyclohexyl carbonate, diheptyl carbonate, dioctyl carbonate, didecyl carbonate or didodecyl carbonate. One exemplary substituted carbonate is glycerol carbonate. Examples of carbonates in which n is greater than 1 comprise dialkyl dicarbonates, such as di-tert-butyl dicarbonate, or dialkyl tricarbonates such as di-tert-butyl tricarbonate. One exemplary aromatic carbonate is diphenyl carbonate. In one particular embodiment, the organic carbonate is a carbonate ester is selected from the group consisting of dimethyl carbonate, diphenyl carbonate, ethylene carbonate, trimethylene carbonate, propylene carbonate, glycerol carbonate, and mixtures thereof.

The pH of the carbonate-containing solution generally ranges from about 7.5 to about 12 (e.g., about 7.5, about 8, about 8.5, about 9, about 9.5, about 10, about 10.5, about 11, about 11.5, or about 12). In one embodiment, for example, the pH of the solution ranges from about 8.5 to about 12 (e.g., about 8.5, about 8.75, about 9, about 9.25, about 9.5, about 9.75, about 10, about 10.25, about 10.5, about 10.75, about 11, about 11.25, about 11.5, about 11.75, or about 12). In one preferred embodiment, the pH of the solution ranges from about 10 to about 12 (e.g., about 10.1, about 10.2, about 10.3, about 10.4, about 10.5, about 10.6, about 10.7, about 10.8, about 10.9, about 11, about 11.1, about 11.2, about 11.3, about 11.4, about 11.5, about 11.6, about 11.7, about 11.8, about 11.9, or about 12).

The carbonate concentration of the solution may vary depending, for example, upon the carbonate chosen (e.g., a carbonate salt or carbonic acid) the desired pH, and/or the hold time of the treatment process. In one embodiment, for example, the carbonate concentration may have a lower limit of about 0.005 mM and an upper limit of the maximum solubility limit of the particular carbonate employed. In another embodiment, the carbonate concentration of the solution is from about 0.005 mM to about 2M. Thus, for example, the carbonate concentration may be about 0.005 mM, about 0.01 mM, about 0.025 mM, about 0.05 mM, about 0.1 mM, about 0.5 mM, about 1 mM, about 5 mM, about 10 mM, about 25 mM, about 50 mM, about 0.1 M, about 0.15 M, about 0.2 M, about 0.25 M, about 0.5 M, about 0.75 M, about 1.0 M, about 1.25 M, about 1.5 M, about 1.75 M, or about 2 M. In one particular embodiment, the carbonate concentration of the solution is from about 0.01 M to about 0.5 M. In another particular embodiment, the carbonate concentration of the solution is from about 0.01 M to about 1 M. In embodiments in which organic carbonate are employed, for example, they may be used as-is (i.e., without dilution or in aqueous forms.

In addition to the carbonate, the solution may contain a buffering agent in order to maintain the pH range within the desired range (e.g., to about 8.5 to about 12) and otherwise modulate the solution concentration. Any buffer can be used in the solutions provided herein so long as it does not adversely affect the carbonate component and supports the requisite pH range required. Exemplary buffering agents include sodium hydroxide, potassium hydroxide, and the like. In one particular embodiment, the buffering agent is sodium hydroxide. Typically, the buffering agent concentration will be 0.005 mM, about 0.01 mM, about 0.025 mM, about 0.05 mM, about 0.1 mM, about 0.5 mM, about 1 mM, about 5 mM, about 10 mM, about 25 mM, about 50 mM, about 0.1 M, about 0.15 M, about 0.2 M, about 0.25 M, about 0.5 M, about 0.75 M, about 1.0 M, about 1.25 M, about 1.5 M, about 1.75 M, or about 2 M. In some embodiments, and dependent upon the buffering agent(s) chosen, and the pH and concentration of the same, the buffering agent may provide a sanitizing benefit to the filter material.

As noted above, treatment of the filter material involves soaking, circulating, recirculating, washing, flushing, passing through, or otherwise contacting the filter material with the solution. In general, any conventional wash or flush method for preparing filter materials for use can be employed. Additionally, or alternatively, filter components such as cellulose pulp or membranes can be treated as described herein prior to fabrication of a device including the filter material. Thus, for example, the filter material may be treated or contacted with the solution for anywhere from 30 seconds to 6 hours, or longer, provided that the length of time does not adversely affect or impair the performance of the filter material.

In one embodiment, the filter material is soaked or immersed in the solution for a period of time (i.e., a static soak). Typically, for example, the filter material is soaked or immersed in the solution for about 1 minute to about 240 minutes (e.g., about 15 minutes, about 30 minutes, about 45 minutes, about 60 minutes, about 75 minutes, about 90 minutes about 105 minutes, about 120 minutes, about 135 minutes, about 150 minutes, about 165 minutes, about 180 minutes, about 195 minutes, about 210 minutes, about 225 minutes, or about 240 minutes). In one particular embodiment, the filter material is soaked or immersed in the solution for about one minute to about 180 minutes (e.g., about 15 minutes, about 30 minutes, about 45 minutes, about 60 minutes, about 75 minutes, about 90 minutes about 105 minutes, about 120 minutes, about 135 minutes, about 150 minutes, about 165 minutes, or about 180 minutes). In another particular embodiment, the filter material is soaked or immersed in the solution for about 60 minutes to about 120 minutes (e.g., about 60 minutes, about 75 minutes, about 90 minutes about 105 minutes, or about 120 minutes).

In another embodiment, the method includes recirculation of the solution through the filter material, e.g., two or more passes of the solution through the filter material via a pump system. An exemplary recirculation arrangement is described in Example 1 and FIG. 2 . Use of conventional filtration, tangential flow filtration, and similar methods can be readily applied to recirculation embodiments described herein. For example, average system hold up in a depth filter train is on the order of about 10 L/m2 to about 100 L/m2. In one particular embodiment, the average system hold up is about 10 L/m2 to about 60 L/m2; for example, 25 L/m2 to about 60 L/m2.

It will be understood that the above pH, carbonate concentrations, and contact/circulation regimes can be optimized to provide maximum reduction of leachable beta-glucans (see, e.g., Example 2). For example, in certain cases higher pH (e.g., 10 to 12) and higher contact time (e.g., 80 to 120 minutes) at lower concentrations (e.g., 0.01 M to 0.5 M) can be particularly effective in reducing leached beta-glucan levels. By way of another example, lower pH (e.g., 7.5 to 10) may require higher molarities (e.g., 0.5 M to solubility limits) for most effective reduction of leachable beta-glucan levels. By way of yet another example, extended hold times (>80 minutes) can be particularly effective for reducing leached beta-glucans to under 100 pg/ml with pH 11-12 solution at less than 0.5 M carbonate concentration. By way of yet another example, lower pH (e.g., 7.5-10), higher carbonate concentrations (>0.8 M), and lower static hold times (e.g., 1-20 minutes) can be particularly effective in reducing leached beta-glucan levels. In one particular embodiment, the solution has a carbonate concentration of 0.01 M to 1 M, a pH of 10 to 12, and the filter material is immersed in a static soak for 100 to 120 minutes. In another particular embodiment, the solution has a carbonate concentration of 0.01 M to 0.5 M, a pH of 11 to 12, and the filter material is immersed in a static soak for 80 to 120 minutes.

The pressure of the treatment regime (e.g., in a pass or flow-through or (re)circulation arrangement) is not narrowly critical, provided that the pressures do not adversely affect or impair the performance of the filter material and/or removal of leachable beta-glucans.

Cellulose-Containing Filter Material

In general, the methods described herein for removing leachable beta-glucan described herein may be employed with any cellulose-containing filtration or solid support material, media, or membrane, which may pose a risk of leaching beta-glucans into a desired product. As described in further detail herein, the treatment can be carried out either before or after formation of a filtration device (e.g., including a housing for the filter material), both before and after formation of the filtration device, before filtration of a desired product (i.e., as a pre-treatment), and combinations and multiples thereof. Thus, another aspect of the present disclosure is a cellulose-containing filter material treated in accordance with the methods described herein, wherein the filter material has a reduced amount of leachable beta-glucans as compared to an untreated filter material.

As a cellulose-containing filter material, the filter material may include cellulose fibers (e.g., wood pulp and/or cotton derived), regenerated cellulose fibers, cellulose fibers combined with inorganic filter aids (e.g. diatomaceous earth, perlite, fumed silica), cellulose fibers combined with inorganic filter aids and organic resins, cellulose/silica blends, cellulose derivatives such as cellulose acetate or cellulose triacetate, or any combination thereof. These materials and their methods of making them either by a wet process (similar to papermaking) or a dry process are well known in the art.

In some embodiments, for example, the filter material is a depth filter or will be used to ultimately form a depth filter device. Representative commercially available depth filters which may be used in accordance with the treatment methods herein include, for example, 3M/CUNO AP series depth filters (AP01); 3M/CUNO CP series depth filters (CP10, CP30, CP50, CP60, CP70, CP90), 3M/CUNO HP series depth filters (HP10, HP30, HP50, HP60, HP70, HP90), 3M/CUNO CA series depth filters (CA10, CA30, CA50, CA60, CA70, CA90), 3M/CUNO SP series depth filters (Examples include SP10, SP30, SP50, SP60, SP70, SP90); 3M/CUNO Delipid and Delipid Plus filters; 3M/CUNO Polynet Filters (Polynet-PB); 3M/CUNO Life Assure filters; EMD Millipore CE series depth filters (CE15, CE20, CE25, CE30, CE35, CE40, CE45, CE50, CE70, CE75); EMD Millipore DE series depth filters (DE25, DE30, DE35, DE40, DE45, DE50, DE55, DE560, DE65, DE70, DE75); EMD Millipore HC filters (A1HC, B1HC, COHC, D0HC, X0HC, VPF, F0HC), Clarisolve (40MS, 20MS); EMD Millipore Corporation Clarigard®, Polygard®, Millistak+®, and Polysep® filters; ManCel Associates depth filters (PR 12 UP, PR12, PR 5 UP), and PALL Corporation filters (Bio20, SUPRA EKIP, KS-50P); Sartorius AG filters (Sartobran®); and the like.

In other embodiments, the filter material is a wood pulp.

Other filter materials and devices that can be treated in accordance with the methods described herein include absorbents, ultrafiltration membranes, dialyzers, and like materials containing cellulose or derivatives thereof. Again, such materials may be treated as described herein either before or after (or both before and after) formation of the commercial filtration device.

Biopharmaceuticals and Plasma Derivatives

As noted above, cellulose-containing media and filters are widely used in biopharmaceutical and plasma purification processes for removal of impurities from target molecules. Accordingly, another aspect of the present disclosure is a method for preparing a biopharmaceutical or a plasma derivative having a reduced amount of leached beta-glucan, the method comprising treating the biopharmaceutical or a plasma derivative by contact with a cellulose-containing filter material treated in accordance with any preceding method of treatment claim. Yet another aspect of the present disclosure is a biopharmaceutical or a plasma derivative prepared in accordance with the aforementioned method.

In general, conventional methods for preparing (i.e., filtering) biopharmaceutical or a plasma derivatives may be employed, except that standard filters and filter materials are replaced with the treated cellulose-containing filter materials described herein.

The biopharmaceutical or a plasma derivative that may be prepared/purified using the methods described herein is not narrowly critical; any suitable biopharmaceutical or a plasma derivative that is commonly filtered as described herein may be employed. By way of illustration, blood factors (e.g., Factor VIII and Factor IX), thrombolytic agents (e.g., tissue plasminogen activator), hormones (e.g., insulin, glucagon, growth hormone, gonadotrophins), haematopoietic growth factors (e.g., erythropoietin, colony stimulating factors), interferons (e.g., interferons-α, -β, -γ), interleukin-based products (e.g., interleukin-2), vaccines (e.g., hepatitis B surface antigen), monoclonal antibodies (many known examples), and other products (e.g., (tumor necrosis factor, therapeutic enzymes), and the like are contemplated.

Having provided the disclosure in detail, it will be apparent that modifications and variations are possible without departing the scope of the invention defined in the appended claims. Furthermore, it should be appreciated that all examples in the present disclosure are provided as non-limiting examples.

EXAMPLES

The following non-limiting examples are provided to further illustrate the present disclosure. It should be appreciated by those of skill in the art that the techniques disclosed in the examples that follow represent approaches the inventors have found function well in the practice of the subject matter disclosed herein, and thus can be considered to constitute examples of modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments that are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.

Example 1: Investigation of Different Flushing Chemistries for Removal of Beta-Glucan from Depth Filtration Media

In this example five specialized flushing chemistries were tested for removal of beta-glucans from cellulosic depth media. The investigated chemistries included 2 M sodium chloride, 4 M urea, 1M sodium carbonate buffer pH 10, 0.5N sodium hydroxide and RODI water (Milli Q). Solutions were prepared and sterile filtered prior to use. Experiments were performed on Viresolve Pre Filter (VPF) micro devices with 5 cm² membrane area (OptiScale 40 Capsule Cat No SSPVA40NB9). Experimental setup included an automated data collection system (DAQ 2.0) for collecting pressure drop and flowrate data, platinum cured silicon tubing flow path (Cat No #HV-96410-14, Cole Parmer, IL, USA), single use pressure transducers (PDKT-104-03, Pendotech, NJ). Four trains were setup in parallel. Schematic of experimental setup is shown in FIG. 1 .

The filter was flushed with 100 L/m² of specialized flush solution followed by static hold for 1 hr. At the end of hold time the filter was flushed with 400 L/m² of purified water at 600 LMH.

Post RODI flush the filter was equilibrated with 30 L/m² equilibration buffer (25 mM Tris pH 7). Post equilibration 30 L/m² of monoclonal antibody solution was loaded and the filtrate was collected into 15 ml polystyrene centrifuge tubes. These samples were analyzed for leached beta-glucan using a Charles River PTS Rapid Micro Method Glucan assay. The standard flush, which was used as a control, included 100 L/m² RODI flush followed by 30 L/m² Buffer equilibration. Table 1 summarizes the process. Flux for all steps was set at 360 L/m²·hr.

TABLE 1 Summary of flushing strategy Standard Flush (L/m²) Flush Hold Buffer 25 Protein Volume time mM Tris solution Flush Solution (L/m²) (hrs.) RODI pH 7 (L/m²) Control 0 0 100 30 30 (Standard Flush) Water (control) 100 1 400 30 30 4M Urea 100 1 400 30 30 2M Sodium 100 1 400 30 30 Chloride 1M Carbonate 100 1 400 30 30 solution pH 10 0.5N Sodium 100 1 400 30 30 Hydroxide

Experimental setup for the recirculation mode is shown in FIG. 2 . In recirculation mode, a defined amount of flushing buffer was dispensed in the feed tank. Outlet of the depth filter to be flushed was placed in the feed tank. Flushing was performed at a defined flowrate and for a defined time. Same equipment setup and filters as flow through mode were used for recirculation study described above, with the main difference being that the filter outlet was directed back to feed tank in recirculation mode. The three levels investigated include 25 L/m², 50 L/m² and 60 L/m². All three volume to area ratios reduced the leached beta glucan levels to 100-200 pg/ml range and were effective.

Protein pools collected at a protein solution volume to filter area ratio of 30 L/m² were tested for beta-glucan levels. Confirmatory runs were performed using a second VPF lot. For both the lots, the reduction in beta-glucan leachables in the product pool was greater than 80% (compare light green bar (control, standard flush) with dark green (1 M carbonate flush)). The results are shown in FIG. 3 .

To ensure that specialized flushing strategy using 1 M sodium carbonate pH 10 solution does not negatively affect Viresolve Pre Filter absorptive capacity was tested a comparative performance test was performed. Viresolve Pre Filter (VPF) Devices flushed with standard flush (control) and specialized flush were used as pre filters for Viresolve Pro Filters. Viresolve Pro flux profiles were compared to investigate any impact of the specialized flush on pre filter performance. This test was performed on two different lots of VPF and capacities were tested on two different monoclonal antibody feeds. No detrimental impact on VPF absorptive capacity was observed in either of the two cases. Results are shown in FIG. 4 and FIG. 5 .

Example 2: Investigation of Specialized Flush Parameters on Beta-Glucan Removal Efficiency 1. Effect of Carbonate Counter Ion

Analysis of carbonate counter ion was performed to evaluate operational feasibility of its usage as a flushing solution for beta-glucan removal. Primary criteria selected for the analysis were toxicity, solubility and other operational concerns. A summary of exemplary investigated counter ions is provided in Table 2.

TABLE 2 Analysis of counter ions Carbonate Solubility Cation Toxicity (gm per 100 gm water) Sodium(Na⁺) Low (irritant) 21.5 Potassium (K⁺) Low 111 Calcium (Ca²⁺) Non toxic 7.753 × 10⁻⁴ (Argonite) Carbonic acid NA NA Ammonium (NH₄ ⁺) Irritant 10 Organic Carbonates Non toxic/low toxicity High Magnesium (Mg²⁺) Non toxic 0.039 Manganese (Mn²⁺) Non toxic 4.877 × 10⁻⁵ Iron (Fe²⁺) Not available 6.554 × 10⁻⁵ Barium (Ba²⁺) Intermediate toxicity 1.409 × 10⁻³ (2 on NFPA704)

As shown above sodium (Na⁺) and potassium (K⁺) are the most preferred counter ions based on toxicity, solubility and other operational concerns. Calcium in combination with carbonic acid can be used but have operational challenges associated to carbon dioxide sparging. Ammonium (NH₄ ⁺) carbonate can be used for pump treatment but usage in GMP environment can be challenging as it is strong irritant. Organic carbonates can also be used. Other counter ions like magnesium, manganese, iron have limited solubility and barium carbonate is toxic as well as has low solubility. Experiments were performed to compare the sodium and potassium counter ions in removal of beta-glucans from depth filtration media.

Experimental sodium and potassium carbonate were investigated for removal of beta-glucans from depth filter. In case of both sodium and potassium carbonate flushes 0.5 M concentration solution at pH 10 were used. 100 L/m² solution flush was performed at 200 LMH flux. No static hold was performed. After solution flush, 400 L/m² water flush was performed at 600 LMH. Filters were then conditioned with 50 mM acetate buffer 80 mM sodium chloride pH 5.5 buffer by flowing through 30 L/m² of buffer at 600 LMH. Post buffer flush 30 L/m² monoclonal antibody feed was loaded at 100 LMH as a model protein. This protein load was collected and analyzed for leached beta-glucans. Charles River PTS Rapid Micro Method Glucan assay was used for beta-glucan analysis. As shown in FIG. 6 , both sodium and potassium carbonate showed comparable performance for removal of beta-glucans from depth media.

2. Effect of Solution Concentration, pH and Static Hold Time

A design of experiment (DOE) was performed to identify effective range for pH, concentration and static hold time. A Box Behnken design was selected for the study. List of parameters and associated levels are shown in Table 3.

TABLE 3 List of parameters and associated levels Variables Low Mid High pH 7.5 10 12 Concentration (M) 0.01M 0.5M 1M Contact time (min) 10 min 60 min 110 min

For all the runs standard flushing procedure described below was followed. All filters used were of same type and same lot (Viresolve Pre Filter OptiScale 40 Capsule Cat No SSPVA40NB9, Lot No C6BA18393)). 100 L/m² specialized solution flush was performed at 200 LMH flux with the given concentration and pH. Static hold was performed for the given time as per DOE. After static flush, 400 L/m² water flush was performed at 600 LMH. Filters were then conditioned with 50 mM acetate buffer 80 mM sodium chloride pH 5.5 buffer by flowing through 30 L/m² of buffer at 600 LMH. Post buffer flush 30 L/m² monoclonal antibody feed was loaded at 100 LMH as a model protein. This protein load was collected and analyzed for leached beta-glucan concentration. Charles River PTS Rapid Micro Method Glucan assay was used for beta-glucan analysis.

To compare the effectiveness of carbonate flush relative to water a negative control experiment was performed. For water control experiment 100 L/m² water was flushed through the filter at 200 LMH. Static hold for 60 minutes was performed. After static flush, 400 L/m² water flush was performed at 600 LMH. Filters were then conditioned with 50 mM acetate buffer 80 mM sodium chloride pH 5.5 buffer by flowing through 30 L/m² of buffer at 600 LMH. Post buffer flush 30 L/m² monoclonal antibody feed was loaded at 100 LMH as a model protein. This protein load was collected and analyzed for leached beta-glucan concentration. Charles River PTS Rapid Micro Method Glucan assay was used for beta-glucan analysis.

In addition to water control a standard flush experiment was also performed. This was done for comparing the specialized flush results with what is currently used in industry. For standard flush, flushing procedure included 100 L/m² of water flush followed by 30 L/m² of buffer flush both performed at 600 LMH. Post buffer flush 30 L/m² monoclonal antibody feed was loaded at 100 LMH as a model protein. This protein feed was collected and tested for leached beta-glucan content.

Glucan concentrations obtained from the study are shown in Table 4.

TABLE 4 Effect of concentration, static hold time and pH of sodium carbonate solution for beta-glucan removal. % reduction % Beta- reduction glucan Beta- Content glucan compared Concentration to compared Solution Beta- standard to Run concentration Solution Static hold glucan flush water Number (M) pH time (min) Concentration control control 1 1 10 10 166.5 68 78 2 0.505 12 10 134 74 83 3 0.505 12 110 135.5 74 82 4 1 7.5 60 394.5 25 49 5 0.505 10 60 195 63 75 6 0.01 7.5 60 625.5 −19 19 7 0.5 7.5 10 313.5 40 59 8 0.5 10 60 169.5 68 78 9 0.5 10 60 162 69 79 10 0.01 10 10 196.5 63 74 11 1 10 110 203.5 61 74 12 0.5 7.5 110 585 −12 24 13 0.01 10 110 155.5 70 80 14 1 12 60 212 60 72 15 0.01 12 60 125 76 84 16 Water Flush 769 17 Standard flush 524

DOE was analyzed for identifying the significant parameters and their impact on the removal of beta-glucans from depth media. Analysis of variance was performed to identify the parameters which are statistically significant in the model. Solution pH was identified as the most significant process variable and solution concentration did not have significant impact by itself but pH and concentration interaction term was significant. Linear and squared terms for static hold time did not have a statistically significant effect on the leached beta-glucan but the interaction term pH*static hold time was significant. Size of effects for different terms are shown in Pareto Chart in FIG. 7 . Terms represented by blue bars were statistically significant.

Regression equation representing the relationship between levels of beta-glucan which can potentially leach into protein and the factors analyzed in the DOE is given by Equation 1.

beta-glucan=3154−908 Concentration−536.7 pH+7.54 Static Hold Time+107.8 Concentration*Concentration+23.84 pH*pH−0.00854 Static Hold Time*Static Hold Time+72.9 Concentration*pH+0.782 Concentration*Static Hold Time−0.631 pH*Static Hold Time   (1)

Plot of predicted versus measured leached beta-glucan concentration is shown in FIG. 8 .

Contour plots were generated to visualize the effect of parameters with three hold conditions as shown in Table 5.

TABLE 5 Hold values for contour plots Concentration Static hold Hold Level pH (M) time (min) Low 7.5 0.001 10 Intermediate (Center) 10 0.5 60 High 12 1 110

Contour plot for low hold values is shown in FIG. 9 . pH* concentration plot (top, left) shows at hold time of 10 minutes, leached beta-glucan concentration of can be reduced to 100-200 pg/ml range by solution pH greater than 10. Lower pH carbonate solution (<10) require higher concentration (>0.5 M) to reduce levels of leached beta-glucans. Static hold time* concentration plot (top, right) show low pH carbonate solution (pH 7.5) require concentration greater than 0.7 M to remove beta-glucans. Static hold time* pH plot (bottom, left) show that that at solution concentration of 10 mM, significant reduction in leached beta-glucans can be achieved at pH 9 or higher. Also under these conditions static hold time did not significantly impact the reduction in leached beta-glucan. Highest removal was achieved at pH 11 or higher with extended static hold times 80-110 minutes.

For Intermediate hold values the contour plots are shown in FIG. 10 . pH* concentration plot (top, left) shows carbonate solution at pH 9.5 or greater is effective in reduction of leached beta-glucan across entire investigated solution concentration range (0.001 M to 1M) at 60 minute static hold time. pH 10 carbonate solution was effective in reduction of leached beta-glucan effectively over the entire hold time and concentration range as shown in static hold time *concentration plot (top, right). Static hold time * pH plot (bottom, left) shows that the pH 9.5 or higher is effective in reduction of leached beta-glucans at 0.5M concentration independent of static hold time.

For high hold values the contour plots are shown in FIG. 11 . pH* concentration plot (top, left) shows carbonate solution at pH 9.5 or greater is effective in reduction of leached beta-glucans across entire investigated solution concentration range (0.001M to 1M) at 110 minute static hold time. Additionally pH 11-12 and concentration 0.001 M to 0.5 M range can reduce the leached beta-glucan concentration to below 100 pg/ml. pH 12 carbonate solution was effective in removing beta-glucans effectively over the entire hold time and concentration range as shown in static hold time *concentration plot (top, right). Concentration below 0.5M at pH 12 at static hold time greater than 75 minutes was most effective for removing beta-glucans. Static hold time * pH plot (bottom, left) shows that solution concentration of 1M, pH 8.5 or higher is effective in reducing leached beta-glucan levels to below 200 pg/ml.

3. Evaluation of Flushing in Recirculation Mode

In this study we investigated if flushing can be carried out in a recirculation mode as compared to flow through mode as in case of Example 1 and Section 1 and 2 of Example 2. Recirculation mode can help reduce the solution volume needed to perform the flush on depth filters installed in a GMP setting.

Three different volume to area ratios were tested in recirculation mode. 25 L/m², 50 L/m² and 100 L/m². Solution flush was performed at 200 LMH flux. No static hold was performed. After solution flush, 400 L/m² water flush was performed at 600 LMH. Filters were then conditioned with 50 mM acetate buffer 80 mM sodium chloride pH 5.5 buffer by flowing through 30 L/m² of buffer at 600 LMH. Post buffer flush 30 L/m² monoclonal antibody feed was loaded at 100 LMH as a model protein. This protein load was collected and analyzed for leached beta-glucan. Results are shown in FIG. 12 . All three volume to area ratio were able to reduce the levels of leached beta-glucan to 100-200 pg/ml range. The water control and standard flush data shown in FIG. 12 is from Example 2 Section 2.

Example 3: Reduction Beta-Glucan from Cellulose Pulp Used for Filter Media

In this example, effectiveness of potassium carbonate and sodium carbonate for reduction of beta-glucan from cellulose pulp used to make filter media was investigated. Pulp was received in form of flat sheets. 47 mm discs were punched out using a 47 mm Arch Punch. Discs were installed in Millipore Corporation stainless steel filter holder CAT No XX4404700. One disc was installed in each holder. Four parallel filtration trains were set up using automated data acquisition system for collecting pressure and flowrate data similar to Example 1 and 2. 0.5 M sodium carbonate pH 10 and 0.5 M potassium carbonate pH 10, 0.5 N sodium hydroxide were tested during this study. Water was used as a negative control.

Flushing sequence included 100 L/m² solution flush (water in case of negative control) was performed at 200 LMH flux. 60 minute static hold was performed. After static hold, 400 L/m² water flush was performed at 600 LMH. Pulp was conditioned with 50 mM acetate buffer 80 mM sodium chloride pH 5.5 buffer by flowing through 30 L/m² of buffer at 600 LMH. Post buffer flush 30 L/m² monoclonal antibody feed was loaded at 100 LMH as a model protein. This protein load was collected and analyzed for leached beta-glucans. Charles River PTS Rapid Micro Method Glucan assay was used for beta-glucan analysis. The sodium and potassium carbonate flush were able to reduce leached beta-glucan levels by 620 pg/ml and 2110 pg/ml respectively. 0.5N NaOH resulted in increase the leached beta-glucan level. Results are shown in FIG. 13 . 

What is claimed is:
 1. A method for reducing the amount of leachable beta-glucans in a cellulose-containing filter material, the method comprising treating the filter material with a solution comprising a carbonate salt, an organic carbonate, or carbonic acid.
 2. The method of claim 1, wherein the carbonate salt is selected from the group consisting of ammonium carbonate, ammonium hydrogen carbonate, barium carbonate, calcium carbonate, iron carbonate, lithium carbonate, magnesium carbonate, manganese carbonate, potassium carbonate, potassium hydrogen carbonate, sodium carbonate, sodium hydrogen carbonate, and mixtures thereof.
 3. The method of claim 2, wherein the carbonate salt is selected from the group consisting of ammonium carbonate, calcium carbonate, iron carbonate, magnesium carbonate, manganese carbonate, potassium carbonate, sodium carbonate, and mixtures thereof.
 4. The method of claim 3, wherein the carbonate salt is selected from the group consisting of ammonium carbonate, calcium carbonate, potassium carbonate, sodium carbonate, and mixtures thereof.
 5. The method of claim 4, wherein the carbonate salt is sodium carbonate, potassium carbonate, or a mixture thereof.
 6. The method of claim 1, wherein the organic carbonate is a carbonate ester is selected from the group consisting of dimethyl carbonate, diphenyl carbonate, ethylene carbonate, trimethylene carbonate, propylene carbonate, glycerol carbonate, and mixtures thereof.
 7. The method of claim 1, wherein the pH of the solution is in the range from about 7.5 to about
 12. 8. The method of claim 7, wherein the pH of the solution is in the range from about 8.5 to about
 12. 9. The method of claim 8, wherein the pH of the solution is in the range from about 10 to about
 12. 10. The method of claim 1, wherein the carbonate concentration of the solution is from about 0.01 M to about 0.5 M.
 11. The method of claim 1, wherein the carbonate concentration of the solution is from about 0.01 M to about 1 M.
 12. The method of claim 1, wherein the treatment comprises immersing the filter material in the solution for about 1 minute to about 240 minutes.
 13. The method of claim 12, wherein the treatment comprises immersing the filter material in the solution for about 60 minutes to about 120 minutes.
 14. The method of claim 1, wherein the filter material includes cellulose fibers (e.g., wood pulp and/or cotton derived), regenerated cellulose fibers, cellulose fibers combined with inorganic filter aids (e.g. diatomaceous earth, perlite, fumed silica), cellulose fibers combined with inorganic filter aids and organic resins, cellulose/silica blends, cellulose derivatives such as cellulose acetate or cellulose triacetate, or any combination thereof.
 15. The method of claim 1, wherein the filter material is a depth filter material.
 16. The method of claim 1, wherein the filter material is a depth filter comprising a housing.
 17. The method of claim 1, wherein the filter material is a wood pulp.
 18. A cellulose-containing filter material treated in accordance with claim 1, wherein the filter material has a reduced amount of leachable beta-glucans as compared to an untreated filter material.
 19. A method for preparing a biopharmaceutical or a plasma derivative having a reduced amount of leached beta-glucan, the method comprising treating the biopharmaceutical or a plasma derivative by contact with a cellulose-containing filter material treated in accordance with claim
 1. 20. A biopharmaceutical or a plasma derivative prepared in accordance with the method of claim 19, wherein the biopharmaceutical or a plasma derivative comprises a reduced amount of leached beta-glucans as compared to an untreated biopharmaceutical or a plasma derivative. 